2019-2020 Recycle Case Studies from a Large Service Company
This article lays out what the authors see as the three main water-treatment specification bands and their experiences over the last 18 months.
It should be noted that we work for Select Energy Services, which is the largest watermanagement service and midstream company in the industry and also the owner of the industry’s largest oil-field chemical-supply company. With that comes opportunity to see a broad span of applications and technologies.
While there are no house-developed internal methodological solutions that must be used, deliberate effort was taken to stay chemically and technologically agnostic—which has allowed a broad spectrum of systems applications and observations.
This article by no means represents the total of all treatment approaches currently in use. Indeed, there are many credible paths to operator reuse goals. Our intention is to describe the paths we encountered and used.
Treatment and reuse of produced water in the oil field has changed in the last few years. With some zone exceptions, five years ago hydraulicfracturing (frac) operations were typically 100 percent fresh-water based.
Today, it is rare to find a frac that does not involve at least some recycled produced water. This applies to all regions to some degree, with the biggest change of late occurring in the biggest region—the Permian.
The reasons for this major shift to using recycled water include:
• A more factory approach of production, which has eased the notable logistics costs of reliably moving water from one point to another. The most expensive aspect of recycling water is the logistics and economy of scale, and this has much improved.
• The shift to slickwater fracs, which are more forgiving of lesser Key Performance Index (KPI) treatment programs.
• The overstress of areas, which are becoming overwhelmed, at economically keeping up with water usage and water-disposal demands.
• The growth of the majors and ability to have deeper life-cycle analysis, combined with a growing trend for real commitments to sustainability programs.
The methods for recycling have evolved. There is still no standardized method, though the overall trend of oxidize and separate is the core of what is done most today—with a great many variants. This is partly because there is no standardized water-quality specification (spec) or KPI. The reasons for this will be described.
State of KPI
The Key Performance Indexes are quality standards the water must meet from a recycle/reuse program (i.e. maximum pH, ppm of components, etc.). At present, the industry does not have a standardized KPI. It may never.
The KPI needs are set by a wide list of factors, the most volatile of which is the operator/customer understanding of what is truly needed. The industry as a whole is continuing to learn.
There is also a trend of operators consolidating into larger corporations, with majors able to have sufficient in-house expertise and analysis focusing on KPI refinement for overall project optimization.
For smaller operators, that same goal may be met by working with more experienced service companies who can provide expertise via the understanding of hydraulic fracturing, frac chemistry, well testing and decline-curve behavior. Add to that the understanding of the treatment technologies.
One aspect that is not always appreciated is that contaminants in the water interact and either amplify or dampen each other. For example, a saturated water of more than 290,000 ppm total dissolved solids (TDS) can actually have a working frac package behave much worse with freshwater dilution. This is because ion behavior and interactions change as the relative ratio of that ionto-water availability changes.
The water-treatment KPI needs for a successful frac package should in some ways be viewed as a multidimensional continuum. Consider it as a barrier field between acceptable and troubled frac operations.
The field could be 10 or even more dimensions. For example, a water that passes an iron spec of 20 ppm may operate just fine. However, if it is then combined with a high barium fresh water and sent to frac, the barium can amplify irons behavior potentially damaging the frac package, even if it is in spec.
Or the other side of that example, a spec set at very low iron, but the whole time is used in a setting without barium (or many other types of ions), will have been a more expensive and more difficult recycle program and have strained the project economics unnecessarily. This type of example can apply to many of the items in a typical KPI.
One aspect that is not always appreciated is that contaminants in the water interact and either amplify or dampen each other.
Here are some of the main components that will impact the KPI of a water for reuse:
Water KPI Needs Affected by a Frac-Chemistry Program
Cross-link and linear-gel program: These packages are more sensitive to water quality and require more stringent KPI than a slickwater program. Slickwater frac (Friction Reducer [FR]): These are simple chemical packages relative to gel packages. So, are less sensitive to various contaminants and ions in the water. This is currently the predominant chemistry.
Not all FR is created equal. Anionic FR tends to react poorly with certain divalent ions. Cationic FR is less sensitive, but generally more expensive. There are numerous formulations and variations of FR. The Figure 2 chart is a performance array of different loadings of FR tested against varying ratios of produced to fresh water.
Water KPI Needs Affected by Regional Geology Total Dissolve Solids (TDS, or salts content):
The downhole salts will quickly dissolve into and interact with the water and frac package.
Iron content: In particular, can interact with the chemistry and the components in the water.
Other ionic or organic composition: These can affect and interact with the KPI. For example, if fracing into a high barium formation, sulfate concentration starts to matter.
Water KPI Needs Affected by Regional Geography
Freshwater availability: If it is cheap and plentiful, reuse programs can rely on higher dilution ratios and run relaxed KPIs.
Infrastructure capacity: Is this a necessary consumption of the produced water because there are no other options? What kind of volumes are available and where are they needed, and what will that be over days, months and years? All affect the costs of the KPIs and thus the need to move the KPIs and adjust elsewhere for optimized costs.
Water KPI Needs Affected by Duration and Volume of Need (permanent facility versus mobile facility)
Permanent facility: These create better KPI consistency and efficiency, but can be affected by market activity. If the viability of the project is confidently long term, a permanent facility can allow economy of scale for large facilities and lower cost.
However, will the feed rate = capacity of the plant = draw rate without break over years’ worth of operation? The reality of that equation greatly affects the economic viability of more permanent solutions.
Mobile or Semi-Mobile:
An approach that is easily relocated often gives way to a more stringent KPI, but can be cheaper over the averaged real-flow rates, and logistically are more flexible.
Not all FR is created equal. Anionic FR tends to react poorly with certain divalent ions. Cationic FR is less sensitive, but generally more expensive.
Three common treatment approaches and KPIs
One way to view this is to break this into High Spec, Mid Spec and Low Spec.
High Spec: Tends to be most expensive and have the longest deployment time due to the specialty equipment and the need to connect multiple systems. KPI specifications vary, but typically are on the order of:
• < 10 ppm Total Oil and Grease (TOG)
• < 5 ppm Fe
• < 50 ppm TSS
• < 1 ppm H2S
• pH 6-9
• Positive Oxidation Reduction Potential (ORP)
Mid Spec: Often can be done with common oil-field equipment, making it generally less expensive. Since it often has fewer purpose-built specialty equipment, these generally don’t require long-term contracts for capital recovery. Specifications vary, but typically are on the order of: • < 10 ppm TOG • < 5 ppm Fe • < 50 ppm total suspended solids (TSS)
• < 1 ppm H2S
• pH 6-9
• Positive ORP
Low Spec: Generally, field-expedient solutions. They are often without written specifications, but have operation requirements that will, by their nature, mitigate the priority item—be it Fe, TSS, oil, H2S, bacteria, etc. The target water-quality spec varies greatly based on the job and often does not involve strenuous analytical testing and reporting. Correspondingly, these tend to be the fastest field-solutions to deploy and have the lowest cost.
High-Spec case study—Southern Delaware Basin Recycling Facility
An operator, with pipeline infrastructure, an existing saltwater disposal (SWD) well and pit, wanted to reuse owned produced water (PW). A SWD pump permit was not yet issued. That meant 100 percent of the PW entering the SWD was to be treated and stored for reuse. The KPIs for this operation were stringent, partly based on conservative caution and partly based on a corporate mandate of assured no-sheen in the storage pit. KPIs for this project were:
• 25,000 barrels per day (BPD) capacity
• Total Oil & Grease < 10ppm,
• Particle Size < 50 micron
• TSS < 50ppm
• H2S < 1ppm
• ORP > 150 mV
• Daily reporting of oil-field barrels (BBLs) treated and measure of water quality: ORP, H2S, TDS, pH, Fe and turbidity.
An operator, with pipeline infrastructure, an existing saltwater disposal (SWD) well and pit, wanted to reuse owned produced water (PW). A SWD pump permit was not yet issued.
Note the original spec called for ORP > 400, but when analyzing the chemical costs likely needed to achieve this, it was adjusted to a much lower 150 mV ORP. Aeration was added into the storage pond for water preservation and prevention of H2S formation.
There was no biological spec, either, recognizing that would be an expensive add of little benefit since the water remained exposed to contamination while in the open pit. The ORP spec and aeration systems should help manage excessive anaerobic activity.
To meet a tight deadline, this project was done in two phases, with phase 1 being a 15,000 BPD fast deployment with existing equipment and then a plant turnaround in Phase 2 with larger 25,000 BPD purposebuilt systems. This plant was selected as the most cost-effective bid to customer. Both phases were completed, and the plant was successful over the life of the activity at the field location.
Mid-spec case study—Permian Delaware basin recycle project (New Mexico)
The operator had a pipeline infrastructure of produced water that comingled with area commercial midstream sourced produced water. It also had three storage pits. The KPIs for this operation were less severe from the standpoint of cost optimization and ability to have a shorter-term contract with more common fieldexpedient equipment. For this project:
• 40,000 BPD capacity
• Fe < 10 ppm
• TSS < 150 ppm
• Oil and grease < 30 ppm
• pH: 6-8
• H2S < 1 ppm
• 1-5 ppm residual oxidizer on discharge to pit
• Daily reporting along with reporting every four hours on certain KPIs
Data tracking and management is done by a combination of onboard data-logging and telemetry standard to the disinfection chemistry trailer, combined with handheld data-entry systems where the operator manually puts in the frequent readings, levels and analytical entries.
Due to sparse data communications at the location, the data-entry systems are designed to batch and push data automatically, either when that operator returns to the mancamp or when his rounds take him into a section that has signal. This facility is still in operation and has fed numerous fracs.
In operation, the water quality is considerably higher than Mid Spec, the KPIs and essentially at the KPI of the High Spec plant. But since it does not have engineered systems in place to assure that in the event of upsets, the plant is only held to the indicated Mid-Spec KPIs.
Low-Spec case study—Various Permian locations (mobile basis)
The operator has large fields with infrastructure and pipelines from which to draw produced water, but no other resources, tank batteries, etc. The scope is to draw the water, oxidize any H2S, gross-oil removal and blend with fresh water being sent to frac.
This is to be accomplished on a mobile-field basis. To this end, multiple deployments are done using mobile gun barrels combined with chemical oxidizer injection systems that track dosing in relation to the water-transfer rate being fed.
The clarified water from the mobile gun barrel then goes into a frac tank batter, which is drawn and sent through an automatic proportioning system (APS). The APS monitors the salt content and flow rate of the oxidized produced water, the salt content and flow-rate of the fresh water, combines them, and then monitors the salt content and flow rate of the combined water going to the frac.
There is relatively little monitoring and reporting from these lowcost expedient field-controlled reuse deployments, but frac operations have been successful. More of these simple solutions are being called for.
As can be seen, due to the widely varied nature of KPI, volumes, water needs and price structure demands, various projects are vastly different in scope and activity. The industry trend seems to be more in the direction of the more economical and logistically simple Low-Spec and some MidSpec treatment.
One driver is the expansion of pipeline infrastructures that allow for reliable produced-water volumes to be delivered to multiple locations. This also means treatment discharge goes directly to the frac, rather than to storage. Water needs only be treated to a KPI suitable for immediate consumption at the frac versus water-treatment KPIs intended for longer-term storage in an exposed pit.
Another reason for the Low- and Mid-spec trend growth is the continued improvement of frac chemistry tolerances to lesser water specifications. Water qualities being used regularly today would have been substantially more difficult to overcome five years ago, and that development is continuing.
Systems for accurately blending the produced to fresh water to assure consistent water composition also continue to improve.
Working with experienced treatment personnel to optimize not only the treatment, but the KPIs and entire frac package, is the best way to optimize the economics.
Authored by Clay Maugans, Ph.D., director of water technologies, Select Energy Services + John Novotny, MBA, director of water treatment, Select Energy Services